The demand for data communication services has exploded with the acceptance and widespread use of the Internet. While data communications have historically been serviced via wired connections, wireless users are now demanding that their wireless units also support data communications. Many wireless subscribers now expect to be able to “surf” the Internet, access their email, and perform other data communication activities using their cellular phones, wireless personal data assistants, wirelessly linked notebook computers, and/or other wireless devices.
Significant performance issues exist when using a wireless network to service data communications. Wireless networks were initially designed to service the well-defined requirements of voice communications. Generally speaking, voice communications require a sustained bandwidth with minimum signal-to-noise ratio (SNR) and continuity requirements. Data communications, on the other hand, have very different performance requirements. Data communications are typically bursty, discontinuous, and may require a relatively high bandwidth during their active portions.
The wireless network infrastructure must support both low bit rate voice communications and the varying rate data communications. More particularly, the network infrastructure must transmit low bit rate, delay sensitive voice communications together with high data rate, delay tolerant rate data communications.
It is therefore desirable to provide a communication system that is capable of carrying both delay sensitive lower data rate voice communications and delay tolerant higher data rate data communications with minimal waste of spectral capacity. Further, it is also desirable to provide a communication system that also services bursty data traffic for a plurality of data users without wasting allocated spectrum.
One example of such a communication system is the Universal Mobile Telecommunications System (UTMS) Terrestrial Radio Access Network (UTRAN). The UTRAN is a third generation system which in some respects builds upon the radio access technology known as Global System for Mobile communications (GSM). UTRAN is a wideband code division multiple access (W-CDMA) system.
A goal of the Third Generation Partnership Project (3GPP) is to evolve further the UTRAN and GSM-based radio access network technologies. Of particular interest here is the support of variable transmission rate services in the third generation mobile radio communications system for both real time and non-real time delay tolerant services. Because users share the same radio resources, the radio access network must carefully allocate resources to individual user equipment (UE) connections based on quality of service requirements, such as variable rate services, and on the availability of radio resources.
For example, in a multimedia session, one bearer may carry a speech connection, another bearer carries a video connection, and a third bearer may carry a packet data connection. Connections are mapped by the UTRAN onto physical transport channels.
Between the UE and the UTRAN, a connection may be mapped to one or more dedicated transport channels (DCHs) or to a common transport channel such as a random access common channel (RACH), a forward access common channel (FACH), a common packet channel (CPCH), a downlink shared channel (DSCH), and a high speed-downlink shared channel (HS-DSCH).
Real time connections are mapped to dedicated channels. On a dedicated channel, resources may be guaranteed to provide a particular service, such as a minimum transmission rate for voice communications. For more information on transport channels, reference should be made to the UMTS 3GPP Specs as follows: 3G TS 25.211, V3.5.0; 3G TS 25.221, V3.5.0; and 3G TS 25.331, V3.5.0, 3G TR 25.848, V0.6.0, 3GPP TR 25.858 V1.0.4, 3GPP TR 25.950 V4.0.0 the disclosures of which are incorporated herein by reference.
To provide effective multimedia capabilities in UMTS, the High-Speed Downlink Packet Access (HSDPA) scheme is being developed which facilitates transfer of packet data to a mobile station at up to e.g. 4 Mbps.
The concept of HSDPA has been standardized in 3GPP for UMTS (cf. 3GP TR 25.858, V1.0.4 January 2002). It considers enhancements that can be applied to UTRA to provide very high-speed downlink packet access by means of a high-speed downlink shared channel (HS-DSCH).
For the basic structure of HS-DSCH two architectures have been considered i.e. an RNC-based architecture consistent with R99 architecture and a node B-based architecture for scheduling. Moving the scheduling to the nodes B enables a more efficient implementation of scheduling by allowing the scheduler to work with the most recent channel information. The scheduler can adapt the modulation to better match the current channel conditions and fading environment. Moreover, the scheduler can exploit the multi-user diversity by scheduling only those users in constructive fades.
In CDMA systems, different signals are transmitted simultaneously within the same frequency band, i.e. the transmit power amplifiers (TPA) have to cope with an input signal obtained by adding a large number of transmit signals for different users and traffic classes. In the multi-carrier case, this input signal is given by the sum of the input signals for several frequency bands. The range of this multi-carrier sum signal must be within the linear range of the TPA input. Also the average power of the multi-carrier sum signal must be a certain amount below a maximum allowed power threshold, to allow for short peak power values to be in the linear range.
In other words, the load put on the TPA has to be monitored and overload situations (i.e. situations where the above conditions are not met) have to be controlled, such that the stability of the network and QoS for user of the network is maintained.
It is therefore an aim of the present invention to provide a method of transmitting of data which prevents overload situations of the transmit power amplifiers and which makes efficient usage of the available transmit power.